1. Field of the Invention
The present invention relates to a power management system for use with a portable information processing apparatus such as a portable information terminal unit that operates with a battery power and in particular, to a power management system for use with a wireless LAN terminal unit that performs a wireless LAN communication corresponding to IEEE 802.11 standard.
2. Description of the Prior Art
A portable LAN terminal unit should use a battery for the power supply. To suppress the power consumption, in the non-operating state, the power cannot be always supplied to the wireless LAN terminal unit. However, when the power of the terminal unit is fully turned off, it takes a long time to start up the wireless LAN terminal unit and its application program. To prevent such a problem, when the wireless LAN terminal unit is not used for a long time, it is normally placed in the suspend state. In the suspend state, the power supplied to the peripheral LSI is shut off (as prior art reference 1) or not shut off (as prior art reference 2) that depends on the characteristic of the peripheral LSI or the system operation. In the prior art reference 2, when data is received, the peripheral LSI (wireless LAN communication LSI) may generate an interrupt signal that causes the CPU to be resumed so as to receive the data.
However, when resuming the wireless LAN terminal unit after the power supplied to the wireless LAN communication LSI corresponding to the IEEE 802.11 standard have been shut off (as the prior art reference 1), in addition to the activation and re-initialization of the LSI, a wireless LAN bridge should be re-connected to the wireless LAN terminal unit. Thus, it takes a time for the wireless LAN terminal unit to return to the communicating state.
On the other hand, when the power supplied to the wireless LAN communication LSI is not shut off (as the prior art reference 2), the power consumption in the suspend state is larger than the power consumption in the power shutoff state. In addition, when the wireless LAN terminal unit is traveled when it is in the suspend state, a connecting process for another wireless LAN bridge is required. In that case, since the CPU cannot use the beacon data transmitted by the former wireless LAN bridge, the wireless LAN terminal unit cannot perform a connection switching process for the other wireless LAN bridge (referred to as xe2x80x9croaming processxe2x80x9d). Thus, after the CPU is resumed, the wireless LAN terminal unit should perform the re-connecting process. Consequently, it takes a long time until the wireless LAN terminal unit can be used. FIG. 1 is a flow chart showing an example of the roaming process which will be explained later.
In a case where the CPU is resumed by an interrupt caused by the peripheral LSI (wireless LAN communication LSI) upon occurrence of the received data (as the prior art reference 2) so that the CPU performs a receiving process, the CPU is resumed so as to perform the roaming process whenever beacon data is periodically received. Thus, the power consumption becomes large.
The present invention has been made to overcome the aforementioned disadvantages and accordingly, has an object to provide a system that allows functions of a wireless LAN terminal unit including a communicating function to be quickly used without need to activate and re-initialize a wireless LAN communication LSI and to re-connect it with a wireless LAN bridge upon reception of beacon data from the wireless LAN bridge when the CPU is suspending.
According to a first aspect of the present invention, there is provided a power management system for use with a wireless LAN terminal unit, the system having: a CPU having a suspend/resume function, a RAM; a power supply; a switch for causing the CPU to be placed in the suspend state or a resume state; and a wireless LAN communication LSI; and roaming processing means for, when the wireless LAN terminal unit travels, performing a roaming process in which a wireless LAN bridge communication with the wireless LAN terminal unit is switched to another wireless LAN bridge, wherein when the CPU is placed in the suspend state, the wireless LAN communication LSI and the roaming processing means are operated by the power supplied by the power supply, and wherein when the CPU is placed is the suspend state, the roaming processing means performs the roaming process.
The power management system may further comprise: power supply controlling means for controlling the power supplied to the wireless LAN communication LSI and the roaming processing means, wherein the RAM has an area for storing information representing whether or not the power should be supplied to the wireless LAN communication LSI and the roaming processing means when the CPU is placed in the suspend state, and wherein the CPU determines whether or not to supply the power to the wireless LAN communication LSI and the roaming processing means through the power supply controlling means corresponding to the information when the CPU is placed in the suspend state.
In the power management system, the roaming processing means may be built in the wireless LAN communication LSI.
The power management system may further comprise: power supply controlling means for controlling the power supplied to the roaming processing means; and a timer, wherein the power supply controlling means uses the timer to supply the power to the roaming processing means in synchronism with the reception time of beacon data periodically transmitted from the wireless LAN bridge so that the roaming processing means performs the roaming process.
In the power management system, the roaming processing means, the power supply controlling means, and the timer may be built in the wireless LAN communication LSI.
In the power management system 1, the roaming process may be a process for executing a wireless LAN bridge connection switching protocol when the reception intensity of newly received beacon data from a new wireless LAN bridge is stronger than the reception intensity of older beacon data from a previous wireless LAN bridge, the reception intensity of older beacon data being stored in the RAM.
These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawings.